World number 116 Taylor Townsend of the United States stunned fourth seed and Wimbledon champion Simona Halep to reach the third round of the US Open.
Townsend fought back from losing the opening set to record a shock 2-6, 6-3, 7-6 win over the Romanian at Flushing Meadows in New York.
The 23-year-old will face Sorana Cîrstea in the the third round after the Romanian beat Spain's Aliona Bolsova 3-6, 6-4, 6-2.
"This means a lot," said Townsend.
"It's been a long journey.
"I had a match point against Kiki Bertens at Wimbledon and close matches this year and not managed to get over the hump.
"This match gives me so much confidence that I can do it.
"I said to myself this was an opportunity to go for it.
"There was nothing to lose."
American teenage star Coco Gauff continued her rise in prominence, booking a third-round place with a 6-2, 4-6, 6-4 victory over Tímea Babos of Hungary.
The 15-year-old will play defending champion Naomi Osaka, who overcame Poland's Magda Linette 6-2, 6-4.
In the men's singles, Alexander Zverev of Germany battled to a five-set win against American Frances Tiafoe.
Zverev, seeded sixth, survived an error-strewn performance to clinch a 6-3, 3-6, 6-2, 2-6, 6-3 victory in a thrilling second-round encounter.
Australian Nick Kyrgios also progressed, with a comfortable 6-4, 6-2, 6-4 triumph over unseeded Frenchman Antoine Hoang.
Spaniard Rafael Nadal, bidding for a fourth US Open title, reached round three after his opponent, Australian Thanasi Kokkinakis, withdrew with a shoulder injury.
Nadal will now take on South Korean Chung Hyeon.